1. Field of the Invention
The present invention relates to a method of assembly of at least two components of ceramic material each having at least one flat surface.
2. Description of the Prior Art
In accordance with this method, the components are permanently assembled together without interposition of cement, of glass or of any jointing material by autogenous welding performed during a heating operation at a temperature higher than or equal to 17OO.degree. C. in a reducing atmosphere.
The invention applies to the fabrication of products for the electronic industry in which it is necessary to provide a product having a predetermined thickness greater than or equal to 1 mm, for example, and electric conductors embedded within the thickness of the product. Two non-limitative examples of products within the field of application of the invention are multilayer substrates and so-called modules or encapsulating packages for semiconductor chips. The basic concept of a multilayer substrate includes within its scope the concept of a network of conductive tracks placed between the ceramic layers. It should be mentioned in addition that the concept of an encapsulating package or module presupposes the existence of connections providing an external access to the chip which is encapsulated within the module and consequently also of metallic tracks which pass through the thickness of the ceramic body.
The fabrication of ceramic objects comprising only a single layer does not present any particular problem. It is in fact known to produce sheets having a thickness of only a fraction of a millimeter as well as objects having a thickness of several centimeters or tens of centimeters. This is only a question of sintering means. On the other hand, the fabrication of ceramic objects comprising at least two components provided with conductive tracks is more difficult from different points of view. From the dimensional viewpoint, it may prove useful to assemble two components because they have a different geometry, for example, but co-sintering of two components of ceramic material pre-fired at 4OO.degree. C. or at 1OOO.degree. C. produces dimensional irregularity as a result of the shrinkage phenomenon. From an electrical standpoint, the brazing of two components which have previously been metallized locally must be carried out with scrupulous care since it is necessary to guard against any short-circuits with the metallic tracks whereas glass bonding is not recommended in microwave technology by reason of the losses involved.